Halo 3, PUBG, and Theater Mode in General

On the May 9th, 2017 Bombcast, Ben mentioned an idea for a post-match map in PUB-Jee where you could see everyone's paths over time. While I like the idea, it got me thinking about just how cool it would be for this game to have a Halo 3 style theater mode, that would locally save a "film" of the entire match that you could open up later and fly a camera around and see where everybody went and when.

From what I remember, the file sizes would be relatively small compared to actual video files, because all the file contained was a little player movement data that would render its self in the game engine. This also got me wondering why more games didn't attempt to replicate this feature as time went on. I, for one, would love to be able to watch some of the "Murder Island" matches after they're done from each of their perspectives with a camera that I can control and see what they may have missed.

That also got me wondering as to why a theater mode like feature hasn't been implemented in more games? What are your thoughts on it in general?

Good news! Exactly what you described is already on the roadmap:

BATTLEGROUNDS will feature both 2D and 3D match replays. During Early Access, we will add the ability for you to replay your match and analyze the play styles of other players. Alongside our 2D replay system, we will also have 3D in-game replays. With the 3D replay system, you will can record your match using a spectator camera system, giving content creators a new way to capture your character’s matches.

Pretty much all source engine games (I think? CS definitely does) have the ability to record demo files. Which is pretty much exactly what you are talking about.